The vast majority of Internet traffic uses stream-based transport protocols such as Transmission Control Protocol (TCP) or Stream Control Transmission Protocol (SCTP). Due to the growing number of end hosts such as smartphones and tablets, which are multi-homed, a variety of protocols have been proposed to improve end-to-end throughput or to enhance connection resilience. Examples for such protocols are Multipath TCP (MPTCP), Multi-connection TCP (MCTCP) and Concurrent Multipath Transfer SCTP (CMT SCTP).
Multipath protocols are usually designed as “end-host-based” protocols, i.e., both end hosts of the connection or session support all signaling needed to establish and tear down the various transport paths. These protocols may operate on various protocol layers. However, to simplify the issues, transport connections are hereafter used for illustration purposes.
End-host-based protocols provide scalability and avoid the need for network-side equipment. However, these protocols exhibit a variety of weaknesses in case one or both end hosts experience a break-before-make mobility event. In such a mobility event, the host has to detach from one network before it may re-attach to another network. For example, some of these weaknesses are (1) if both hosts move to a new Internet Protocol (IP) address at the same time, their signaling messages carrying the update about the respective new IP address would miss each other resulting in connection failure; and (2) if one host moves to a new IP address and the other host resides behind a firewall, the signaling messages of the moving host will be blocked by the firewall. This also results in connection failure. Further, a multi-homed host cannot utilize its multitude of interfaces for multipath operation if the corresponding access networks support different IP protocols, e.g., some access networks support Internet Protocol version 4 (IPv4), other access networks support Internet Protocol version 6 (IPv6), whereas the peer's access network only supports one of these IP protocols. Such situations are very likely to occur with the roll out of IPv6.